1. Field of The Invention
The invention relates to bisphenol compounds and color stable compositions.
2. Brief Description of The Prior Art
Bisphenols are a valuable class of organic compounds employed in a wide variety of applications. Commercial preparation of the bisphenols frequently involves reacting 2 moles of a starting phenol reactant with a carbonyl compound under acid catalyst conditions. For example, the dihydric phenol 2,2 bis(p-hydroxyphenyl) propane (commonly referred to as "bisphenol-A") is commercially prepared by condensing 2 moles of phenol with a mole of acetone in the presence of an acid catalyst. The phenol is present in a molar excess of the stoichiometric requirement. During the condensation, a number of by-products are formed which are contaminants of the desired product, bisphenol-A. These contaminants, carried in the product stream from the condensation reaction zone, include water, trace quantities of acidic materials derived from the catalyst, unreacted phenol and acetone and a number of isomers of bisphenol-A.
Invariably, there are also carried in the product stream trace amounts of metals introduced with reactants or from the apparatus for reaction.
Although very sophisticated procedures have been developed for separating contaminants from the desired bisphenol products and purifying those products, complete elimination would add substantially to the production costs. Therefore, traces of many of these contaminants have been tolerated to a degree.
Representative of methods and process for the preparation of bisphenols are those described in the U.S. Pat. Nos. 4,191,843; 4,766,254; 4,847,433; 5,124,490; and 5,146,007, all of which are incorporated herein by reference thereto.
One contaminant of the bisphenols, such as bisphenol-A, occurs during storage and after preparation. Color bodies result from thermal oxidative reactions of certain phenolic compounds present with the purified bisphenols. These color bodies develop over a period of time, particularly when trace amounts of iron are present to catalyze the oxidation. In an attempt to reduce such oxidations, additives such as sodium phosphate and phthalic anhydride have been added to bisphenols. Although these additives may delay the formation of color bodies with their consequent discoloration of the bisphenol composition, discoloration eventually occurs.
We have now found that bisphenol composition, particularly bisphenol-A, can be stabilized against the formation of some color bodies and consequent discoloration by controlling their iron content. The reduction or elimination of color changes in the product over periods of time is an economic advantage, and for many applications imperative. For example, when the bisphenol is to be used in the synthesis of polymers requiring color standards.